System for feeding portions of material to an injection molding machine

ABSTRACT

The present invention is a system for feeding portions of material to an injection molding machine including a feeding means that can be a screw feeder, an external container, a material hopper with inclined and parallel walls located inside the container, a load cell that is coupled to the material hopper and a controller.  
     The system dispenses portions of material in a given time and for given duration. The system dispenses accurate weight portions. The system controls the portion weight by weighing a number of dispensed portions using loss-in-weight of the hopper, divides the weight to the number of portion and when it need, control the spin of the screw feeder motor.

FIELD AND BACKGROUND OF THE INVENTION

[0001] The present invention relates to a field of a molding machineand, in particular, concerned to a system for feeding portions ofmaterial to a plastic-injection molding machine.

[0002] Several weight feeding apparatus and systems are known. Theseapparatus and systems are for feeding a large quantity of material. Whena small quantity is needed, e.g., coloring material, in a producingsystem, volume methods are used to achieve the needed weight. Volumemethods are used for feeding small quantities because of the difficultyof weighing a few grams in the production area, which is very noisy andshaky.

[0003] Volume feeding methods, which use to achieve weight feeding, havesome disadvantages. The specific gravity of a material can be changede.g., in a new production batch, and therefore a new scaling is needed.The volume-weight scaling is a long process and requires skilledworkers. Moreover, since the fed volume cannot be controlled thevolume-feeding method assumes that the feeding means dispenses equalportions permanently and therefore ignores the material streamingproblems.

[0004] Feeding hopper usually has an outlet to feed the material. Partof the material, the material in the shaft that is perpendicular to theoutlet, does not press on the hopper. This “outlet-shaft” causes anerror in the hopper weighing since the material in the outlet-shaft orat least part of this material is not weighed. Load cells are calibratedwhen weighing such hoppers.

[0005] There is therefore a recognized need for, and it would be highlyadvantageous to have, a system for feeding portions of material to aninjection-molding machine with the ability to accurately weigh feedingof small quantities of material.

SUMMARY OF THE INVENTION

[0006] The present invention is a system for feeding portions ofmaterial to an injection-molding machine with the ability to accuratelyweigh feeding of small quantities of material.

[0007] According to the teachings of the present invention there isprovided, a system for feeding portions of material to an injectionmolding-machine including (a) a feeding means; (b) a container, with afill opening and an outlet, and the container is installed with thefeeding means; (c) a material hopper, with a fill opening and an outlet,and the material hopper is located inside the container; (d) a load cellthat is coupled to the material hopper, and (e) a controller operativefor: (i) calculating the weight of fed material, using the load cell andloss-in-weight method, and (ii) controlling the feeding means.

[0008] According to further features in the described preferredembodiments, the material hopper of the system has a funnel shaped lowerpart and an upper part and wherein the upper part has the samecross-section-area in each vertical level. The upper part of thematerial hopper can have inclined parallel-walls.

[0009] According to further features in the described preferredembodiments, the controller of the system is further operative forcommand the feeding means to dispense at least one portion of materialfrom the material hopper, wherein each portion is dispensed in a giventime and for a given interval of time in order to dispense portions witha predetermined weight.

[0010] According to further features in the described preferredembodiments, the controller is further operative for it calculates theweight of the dispensed portion by (1) dispensing a number of portions;(2) calculating the weight of the number of portions, usingloss-in-weight method, and (3) dividing the weight of the number ofportions to the number of the portions.

[0011] According to further features in the described preferredembodiments, the feeding means is a screw feeder and the controller isfurther operative for adjusting the weight of the further portion byincreasing or decreasing the spin speed of the screw feeder, if theweight of the portion differs from the predetermined weight.

[0012] According to further features in the described preferredembodiments, the outlet of the material hopper is shifted and elevatedfrom the outlet of the container.

[0013] According to yet another aspect of the present invention there isprovided a material hopper for accurate weighing including (a) a funnelshaped lower part with outlet, and (b) a parallel or cylinder wallsupper part wherein the walls can be inclined.

[0014] According to yet another aspect of the present invention there isprovided a method of accurate weighing of a fed portion including (a)storing the material in a material hopper that it's upper part is aninclined cylinder or an inclined parallel walls; (b) feeding apredetermined number of portions; (c) calculating the weight of thenumber of portions, using loss-in-weight of the material hopper using aload cell, and (d) calculating the weight of each portion of the numberof portions by dividing the weight of the number of portions to thenumber of the number of portions. The predetermined number of portionscan be calculating by dividing the sensitivity of the load cell to theestimated weight of the fed portion.

[0015] The present invention successfully addresses the shortcomings ofthe existing technologies by providing a system for feeding portions ofmaterial to an injection-molding machine with the ability to accuratelyweigh feeding of small quantities of material.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In the drawings:

[0017]FIG. 1 is an illustration of a schematic block diagram of thesystem.

[0018]FIG. 2 is an illustration of a systems' cross-section whilematerial is in the material hopper and the system is in a work or readyto work position.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] The present invention is a system for feeding portions ofmaterial to an injection-molding machine with the ability to accuratelyweigh feeding of small quantities of material.

[0020] The principles and operation of the system according to thepresent invention may be better understood with reference to thedrawings and the accompanying description.

[0021] As used herein in the specification and in the claims sectionthat follows, the term “weight-in-loss” refers to a known method forweighing the material that has been dispensed or spent from a hopper, byweighing the hopper before taking from it having a pre-dispensing weightand secondly weighing the hopper after taking from it having anafter-dispensing weight then obtaining a weight-loss of the hopper,which is the weight of the taken material, by subtracting theafter-dispensing weight from the pre-dispensing-weight.

[0022] As used herein in the specification and in the claims sectionthat follows, the term “outlet-shaft” refers to the part of the materialin a hopper that is located in the shaft that perpendicularly to theoutlet of the hopper and do not press on the hopper walls.

[0023] Referring now to the drawings, FIG. 1 illustrates a schematicblock diagram of the system. The system includes a container 10, amaterial hopper 11 located inside the container 10, a load cell 16coupled to the material hopper 11, a controller 13 that calculatesweight according to the load cell 16 information and commands the motor14 of the screw feeder 12 to dispense portions of material into themolding-machine 15.

[0024] The upper part of the hopper 11 has inclined walls. This shapeenables to keep the material in the outlet-shaft, constant by keepingminimal level of material in the hopper. Moreover, the walls of theupper part of the hopper 11 are parallel, for this reason the shape ofeach new space in the hopper 11 that is created by each dispensedportion. Therefore the profile of the material-pressure, in the hopper11, remains constant. The inclined and parallel walls of the hopper 11minimize the weight errors and facilitate the weight calibration.

[0025] The material must be fed to the molding machine inaccurate-weight portions and each portion must be fed in a given timeand in a given duration. To achieve this target the controller 13commands the motor 14 of the screw feeder 12 to start rotating in aspecific spin in the given time for a given duration. Since the giventime and duration of feeding are given by the molding machine 15, thescrew feeder 12 spin is the only variable that can be used to controlthe weight of the fed portion. In the first time, the controller 13 getsa first weight of the hopper 11 from the load cell 16 and commands themotor 14 to rotate the screw feeder 12 for the given duration and agiven spin that is predetermined by the system operator. Afterdispensing a predetermined number of portions the controller 13 gets asecond weight of the hopper 11. The controller 13 obtains the totalweight of the fed portions using the first weight of the hopper 11, thesecond weight of the hopper 11 and loss-in-weight method. The controller13 obtains the portion weight by dividing the total weight to the numberof fed portions. If the portion weight differs from a predeterminedweight, the controller 13 adjusts the portion weight by increasing ordecreasing the spin of the motor 14 of the screw feeder 12, in the nextset of portions. This process can be done sequentially or in apredetermined time.

[0026]FIG. 2 illustrates the systems' cross-section while material is inthe material hopper and the system is in a work or ready to workposition. The material 17 fills the material hopper 11. The material 17is fed through an outlet 18 of the material hopper 11 to a space 19created between the material hoppers' outlet 23 and an outlet 20 of thecontainer 10, from this space 19 the material 17 is fed through thecontainers' outlet 20 to the screw feeder 12. The material hoppers'outlet 18 is shifted from the containers' outlet 20 to enable keepingthe outlet-shaft 21 constant as long as the material level 22 is higherthan the upper end of the outlet-shaft 21 and isolates the materialhopper 11 from noise and shaking which is coming from the screw feeder12 and its' motor 14. The controller 13 commands a refill means 23 torefill the material hopper 11 when the material level 22 reduced to athreshold level. Part of the material 17 is located in the space 19 andacts as a buffer. This buffer isolates the material hopper 11 andprevents noises and shakings of the screw feeder 12 and its' motor 14,to enable an accurate weighing of the material hopper 11 by the loadcell 16.

[0027] It will be appreciated that the above descriptions are intendedonly to serve as examples, and that many other embodiments are possiblewithin the spirit and the scope of the present invention.

What is claimed is:
 1. A system for feeding portions of material to aninjection molding machine comprising: i. a feeding means; ii. acontainer, with a fill opening and an outlet, and said container isinstalled with said feeding means; iii. a material hopper, with a fillopening and an outlet, and said material hopper is located inside saidcontainer; iv. a load cell that is coupled to said material hopper, andv. a controller operative for: i. calculating the weight of fedmaterial, using said load cell and loss-in-weight method, and ii.controlling said feeding means.
 2. The system of claim 1, wherein saidmaterial hopper has a funnel shaped lower part and an upper part andwherein said upper part has same cross-section-area in each verticallevel.
 3. The system of claim 2, wherein said upper part of saidmaterial hopper has inclined parallel-walls.
 4. The system of claim 3,wherein said controller is further operative for: iii. Command saidfeeding means to dispense at least one portion of material from saidmaterial hopper, wherein each said portion is dispensed in a given timeand for a given interval of time in order to dispense portions with apredetermined weight.
 5. The system of claim 4, wherein said controlleris further operative for: iv. calculates the weight of said portion by:1. dispensing a number of portions;
 2. calculating the weight of saidnumber of portions; using loss-in-weight method, and
 3. dividing saidweight of said number of portions to the number of said portions.
 6. Thesystem of claim 5, wherein said feeding means is a screw feeder.
 7. Thesystem of claim 6, wherein said controller is further operative for: v.adjusting the weight of the further portion by increasing or decreasingthe spin speed of said screw feeder, if said weight of said portion isdiffer said predetermined weight.
 8. The system of claim 7, wherein saidoutlet of said material hopper is shifted from said outlet of saidcontainer.
 9. The system of claim 8, wherein said outlet of saidmaterial hopper is elevated from said outlet of said container.
 10. Amaterial hopper for accurate weighing comprising: (a) a funnel shapedlower part with outlet, and (b) a parallel walls upper part.
 11. Thematerial hopper of claim 10, wherein said upper part is inclined. 12.The material hopper of claim 10, wherein said upper part is a cylindershaped.
 13. The material hopper of claim 12, wherein said upper part isinclined.
 14. A method of accurate weighing of a fed portion comprising:i. storing the material in a material hopper that it upper part is aninclined cylinder or an inclined parallel walls; ii. feeding apredetermined number of portions; iii. calculating the weight of saidnumber of portions, using loss-in-weight of said material hopper using aload cell, and iv. calculating the weight of each portion of said numberof portions by dividing said weight of said number of portions to thenumber of said number of portions.
 15. The method of claim 14, whereinsaid predetermined number of portions is calculated by dividing thesensitivity of said load cell to the estimated weight of said fedportion.